Troops, police and paramilitaries "liberated the whole of the centre of Hawija and are continuing their advance," the operation's commander, Lieutenant General AbdelAmirYarallah, was quoted by AFP as saying.

The UN said that an estimated 12,500 people have fled the town since the offensive began on 21 September, but another 78,000 could be still trapped in the town.

Isis set fire to three oil wells near Hawija to slow the advance of US-backed Iraqi forces and Shia militia groups. The Allas oilfield, 35km (20 miles) south of Hawija, was one of the main sources of revenue for the group.

"Terrorists are trying to use the rising smoke to avert air strikes while retreating," explained army Colonel Mohammed al-Jabouri.

Isis used to control larges swathes of Iraq and Syria, but the group has progressively lost several controlled areas due to joint offensives launched in both countries.

The group lost control of Mosul, Iraq's second largest city, this summer. Militants had seized the town in 2014, making it the de-facto capital of their self-declared Islamic Caliphate.

The recapture of Hawija – 230km (140 miles) north of Baghdad – means that Isis now controls only small portions of territories and outposts in the country, along the Syrian border.

In the neighbouring nation, troops continue to advance in Raqqa, the militants' capital in Syria.

An Isis sign is seen on the road at a military airport south of HawijaReuters